A large-scale computer system or a super computer includes a plurality of processing units that operate in parallel. The plurality of processing units are connected by optical interconnection in order to realize high-speed processing.
The optical interconnection provides a plurality of optical channels in many cases. In this case, the optical interconnection is implemented by an optical module (or an optical transceiver) including a plurality of optical transmitters and a plurality of optical receivers, and a plurality of optical fiber transmission lines.
An optical module is requested to be reduced in size in many cases. Therefore, the plurality of optical receivers in the optical module are densely mounted on one circuit board. Similarly, the plurality of optical transmitters in the optical module are densely mounted on one circuit board.
As a related technique, an optical receiver including a photodiode array is proposed (for example, Japanese Laid-open Patent Publication No. 2012-142822). In addition, a technique for improving frequency characteristics of an optical receiver module is proposed (for example, Japanese Laid-open Patent Publication No. 2003-134051 or Japanese Laid-open Patent Publication No. 2001-127561). Further, a technique for improving isolation characteristics between signal lines is improved (for example, Japanese Laid-open Patent Publication No. 2003-224408). Furthermore, a bias circuit that stably operates an APD that receives an optical signal is proposed (for example, Japanese Laid-open Patent Publication No. 2000-244419).
In an optical receiver module in which a plurality of optical receivers are densely mounted on a circuit board, crosstalk between channels may occur. However, in conventional technologies, it may be difficult to suppress the crosstalk between channels. Particularly, in an ultra high-speed transmission system exceeding 25 Gbps, it is difficult to sufficiently suppress the crosstalk between channels in an optical receiver module.